Alta, WY, USA
N71AR
Maule M-5-235C
The aircraft was observed entering a level, counter-clockwise turn approximately 200-300 feet above ground. Witnesses reported observing the right wing separate from the aircraft after approximately three-quarters of the turn, and the aircraft was then observed to descend rapidly to the ground and burn upon impact. Examination of the airframe records indicated that the aircraft's original struts were still installed with a total of 4,945 hours of service and no indication of any significant maintenance. On site examination revealed that the right wing forward lift strut had separated completely at a point approximately eight inches above its inboard end (right main landing gear attach point). Metallurgical examination revealed that the lower inside of the strut at the separation surface was corroded and that fatigue cracking progressed from the corroded area through a portion of the top surface of the strut.
HISTORY OF FLIGHT On October 23, 1995, approximately 1742 hours mountain daylight time, a Maule M-5-235C, N71AR, registered to/operated by Western Air Research, Inc., and being flown by a commercial pilot, collided with terrain during an uncontrolled descent near Alta, Wyoming. The pilot, who was the president and operations officer for the Operator, was fatally injured. The aircraft was destroyed as was a portion of a wood fence, and there was a post crash fire. Visual meteorological conditions existed at the time and a company flight plan was in effect. The flight, which was a bear/elk tracking trip, was to have been operated under 14CFR91, and originated from Driggs, Idaho, approximately 1510. Several witnesses reported observing the aircraft travelling in an easterly direction and then entering a level, counter-clockwise turn estimated at 200-300 feet above ground in the vicinity of the pilot's residence. Approximately three-quarters through the turn the witnesses reported seeing the aircraft's right wing separate from the fuselage after which the aircraft descended rapidly to the ground (refer to attached witness statements). AIRCRAFT INFORMATION The Maule M5-235C was manufactured in 1984 and had accrued a total of 4,945 hours. There was no evidence within the aircraft's airframe log that any of the four lift struts had been replaced during the aircraft's operating life. The only references within the airframe logbook relative to the struts were on 02/01/85 and 04/01/87 where respective entries in the logs stated "checked struts" and "sanded rusty scratches on left front lift strut, primed, and painted." WRECKAGE AND IMPACT INFORMATION The aircraft crashed in an agricultural field. The terrain at the crash site was characteristic of gently rolling, pasture land and the elevation of the ground impact site was approximately 6,475 feet above mean sea level (msl). The latitude and longitude of the site was 43 degrees 46.63 minutes north and 111 degrees 01.35 minutes west respectively (refer to CHART I). The distribution of wreckage was observed to be along a 001/181 degree magnetic bearing line covering a distance of approximately 750 feet. The majority of the aircraft (airframe/engine excluding the right wing) was observed at the southern terminus of the distribution. The aircraft's entire right wing was observed near the north terminus of the wreckage distribution (refer to photograph 01). The forward lift strut remained attached at its outboard wingspar attach point. The aft lift strut was observed to be separated from its outboard wingspar attach point. The inboard end of the wingspar, where it attaches to the carry through in the cabin overhead, displayed minimal damage and the spar to carry through attach bolt was absent. A small impression in the soil was noted a few inches beyond the outboard aft corner of the wing. The impression contained numerous red and blue paint chip fragments matching the paint on the wingtip (refer to photograph 02). A closeup inspection of the inboard (separated) end of the wing's forward lift strut revealed an irregular, jagged separation. The inside surface of the lift strut displayed large areas of rust and corrosion (refer to photograph 03). The remainder of the wreckage, excluding some small fragments and the right wing fuel tank, were located at the southern terminus of the wreckage distribution (refer to photograph 04). A broad, "V" shaped impact scar was noted terminating in an impact crater. The northern half of the ground scar contained numerous red and blue paint chips matching the paint on the left wingtip (refer to photograph 05). The primary (engine) ground impact crater at the south end of the ground scar contained the aircraft's propeller (refer to photograph 06). The aircraft came to rest approximately 55 feet south of the primary ground impact crater, after impacting a wooden fence. The majority of the wreckage was consumed by a post crash fire (refer to photograph 07). Both left wing struts as well as the right wing aft lift strut were located at the aircraft's final resting place. The propeller was removed from the impact crater. Both blades displayed some "S" bending and one blade tip displayed extensive tip curl (refer to photograph 08). The propeller was separated from the engine crankshaft and the engine had been subjected to the post crash fire (refer to photograph 09). An examination of the right main landing gear strut revealed both attach bolts for the forward and aft lift struts. The aft bolt was separated, however, the forward bolt remained attached to an approximate eight inch section of the lower end of the forward right lift strut. The separation surface displayed an irregular, jagged break line. The inside surface of this section of the lift strut displayed large areas of rust and corrosion (refer to photograph 10). The two separated ends of the right wing forward lift strut were then placed side by side to display their fracture surface pattern similarities (refer to photographs 11/12). MEDICAL AND PATHOLOGICAL INFORMATION Post mortem examination of the pilot was conducted by William A. Fogarty, M.D., at Valley Mortuary, Jackson, Wyoming, on October 24, 1995 (reference Autopsy number A-95-42). Toxicological examination of samples from the pilot was conducted by the FAA's Civil Aeromedical Institute. All tests were negative (refer to attached report). TESTS AND RESEARCH Several portions of the aircraft's right wing forward lift strut and associated right wing components were shipped to the Safety Board's materials laboratory for further examination. Visual examination revealed that the right wing forward strut separated at a point approximately 9-10 inches from the lower bolt end, and "extensive corrosion damage concentrated in the lowest portion of the interior" of the strut was observed. Additionally, "the corrosion damage extended slightly past the separation and had completely penetrated the strut wall thickness in some areas adjacent to the separation" on the lower side of the strut. Metallurgical examination revealed that "the fracture in the relatively uncorroded areas (primarily across the top surface of the strut) " displayed "crack arrest position(s), indicative of fatigue cracking" (refer to attached metallurgical report). ADDITIONAL INFORMATION On-site examination of the wreckage was conducted on the afternoon of October 24, 1995, and the wreckage was verbally released to Mr. William Bertles prior to leaving the site. Written wreckage release was accomplished on October 31, 1995, excluding several components which were retained. These items were formally released to Mr. Bertles on December 11, 1995 (refer to attached NTSB Form 6120.15).
the corrosion, consequent fatigue cracking and ultimate separation of the right wing forward lift strut.
Source: NTSB Aviation Accident Database
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